The original application of this 1967 Ferranti circuit can be changed so that it functions as a pass sensor shield for gears and other moving objects.
This Wien bridge oscillator was found in Radio Electronics from the 90s. The circuit uses the 741...
This circuit from a 1970s General Electric publication applies to motors of the series winding type....
This TTL module can be used in counter and many of them can be cascaded to counts up to 99, 999,...